Ferroelectric thin film, method of manufacturing the same, ferroelectric memory device and ferroelectric piezoelectric device

ABSTRACT

A ferroelectric thin film formed of a highly oriented polycrystal in which 180° domains and 90° domains arrange at a constant angle to an applied electric field direction in a thin film plane and reversely rotate in a predetermined electric field.

Japanese Patent Application No. 2002-379418, filed on Dec. 27, 2002, ishereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

In recent years, research and development of a thin film such as PZT orSBT, and a ferroelectric capacitor and a ferroelectric memory deviceusing such a thin film have been extensively conducted. The structure ofthe ferroelectric memory device is roughly divided into 1T, 1T1C, 2T2C,and simple matrix. Since the 1T ferroelectric memory device hasretention time (data retention time) as short as one month due tooccurrence of an internal electric field in the capacitor because of itsstructure, it is considered to be impossible to secure a 10-yearguarantee generally required for semiconductors. The 1T1C and 2T2Cferroelectric memory devices have almost the same configuration as thatof a DRAM, and include a select transistor. Therefore, the DRAMmanufacturing technology can be utilized. Moreover, since the 1T1C and2T2C ferroelectric memory devices realize a write speed equal to that ofan SRAM, small capacity products with a capacity of 256 kbits or lesshave been produced on a commercial basis.

As the ferroelectric material, Pb(Zr,Ti)O₃ (PZT) has been mainly used.PZT having a composition in or near a mixed region of a rhombohedralcrystal and a tetragonal crystal, in which the Zr/Ti ratio is 52/48 or40/60, is used after doping with an element such as La, Sr, or Ca. Thereason why this region is used after doping is to secure reliabilityindispensable for a memory device.

PZT, which has been widely applied to a ferroelectric memory, is a solidsolution of PbZrO₃ and PbTiO₃. In the case where PZT contains Zr at aratio greater than Zr:Ti=52/48, PZT shows a narrow hysteresis shape. Inthe case where PZT contains a greater amount of Ti, PZT shows ahysteresis shape with excellent squareness.

The hysteresis shape immediately after writing data is better in theTi-rich tetragonal region. The Ti-rich tetragonal region is suitable formemory applications if only the hysteresis shape is taken intoconsideration. However, PZT in the tetragonal region has not been putinto commercial use as a ferroelectric memory device since reliabilitycannot be secured.

Among a number of reliability tests, a reliability test called a staticimprint test is the most rigorous test. In this test, a ferroelectricmemory in which data “1” or “0” is written, that is, a ferroelectricthin film polarized at “+” or “−” is allowed to stand at a predeterminedtemperature (85° C. or 150° C., for example) for a predetermined time(100 or 1000 hours, for example), and whether or not the originallywritten data can be read is tested.

As described above, the hysteresis shape immediately after writing datais better in the Ti-rich tetragonal region. However, the Ti-richtetragonal region means that most of the crystal constituent elementsconsist of Pb and Ti.

Pb has a high vapor pressure, and produces PbO vapor at a lowtemperature of about 100° C. as known from the Ellingham diagram.Moreover, Pb has the smallest bond energy with oxygen (38.8 kcal/mol),and tends to cause Pb deficiency to occur in the PZT crystal. Ti has abond energy with oxygen of 73 kcal/mol, which is about twice the Pb-Obond energy. However, since Ti has the smallest atomic weight (47.88)among the constituent elements of PZT, which is about half the atomicweight of Zr (91.224) which is also a B site constituent element, it ismost likely that Ti is scattered during oscillating bombardment whichoccurs during the heat treatment in the static imprint test, whereby Tideficiency tends to occur in the PZT crystal. These defects result inspace charge polarization, and cause imprint characteristics todeteriorate.

Moreover, O deficiency occurs from the charge neutrality principle,whereby Schottky defects occur due to the ionic crystal structure. Thiscauses leakage current characteristics to deteriorate, wherebyreliability cannot be secured.

A reduction of the device size and the thickness of the ferroelectricthin film has progressed accompanying an increase in the degree ofintegration of the ferroelectric memory and the necessity of low voltagedrive. Therefore, in the case of using PZT as the ferroelectricmaterial, it is impossible to utilize the Zr-rich composition used for asmall capacity memory. This makes it necessary to use PZT having aTi-rich composition.

Specifically, since the relative dielectric constant is increased due toa reduction of the film thickness, the hysteresis shape becomesnarrower. Zr-rich PZT has not posed problems relating to reliabilitysuch as imprint characteristics in practical application. However, ifthe hysteresis shape becomes further narrowed, deterioration of imprintcharacteristics will come to the surface. Therefore, in order to makethe hysteresis shape closer to the hysteresis shape used for a smallcapacity memory by decreasing the relative dielectric constant, PZThaving a Ti-rich composition must be used. This causes theabove-described problems to occur. Therefore, it is impossible toincrease the integration of the ferroelectric memory unless the problemsof Ti-rich PZT are solved.

The simple matrix ferroelectric memory device has a cell size smallerthan that of the 1T1C and 2T2C ferroelectric memory devices, and enablesmultilayering of the capacitors. Therefore, an increase in the degree ofintegration and a reduction of cost are expected. A conventional simplematrix ferroelectric memory device is disclosed in Japanese PatentApplication Laid-open No. 9-116107, for example. Japanese PatentApplication Laid-open No. 9-116107 discloses a drive method in which avoltage of one-third a write voltage is applied to unselected memorycells when writing data into the memory cell. However, this technologydoes not describe the hysteresis loop of the ferroelectric capacitornecessary for the operation in detail. The present inventors haveadvanced development and found that a hysteresis loop with excellentsquareness is indispensable to obtain a simple matrix ferroelectricmemory device which can be operated in practice. As a ferroelectricmaterial which can deal with such a requirement, Ti-rich tetragonal PZTmay be considered as a candidate. However, the most important subject isto secure reliability in the same manner as the 1T1C and 2T2Cferroelectric memories.

A ferroelectric thin film used for a ferroelectric memory is generallyused in a state in which the polarization axis of the ferroelectric isaligned in the direction of an applied electric field.

In PZT, the Zr/Ti ratio of 52/48 is called a phase boundary, which is amixed region of a rhombohedral crystal and a tetragonal crystal. If Zrexceeds 52, the crystal structure becomes rhombohedral. If Ti exceeds48, the crystal structure becomes tetragonal.

In rhombohedral PZT, the polarization axis exists along the <001>axis.In tetragonal PZT, the polarization axis exists along the <111>axis.Therefore, in the case of using a PZT thin film for a ferroelectricmemory, the PZT thin film is generally used in a state in which theorientation is aligned with the polarization axis direction, asdescribed in 49th Japan Society of Applied Physics and Related SocietiesMeeting Preliminary Report 27a-ZA-6.

However, domains which are sources of ferroelectricity are present inthe ferroelectric in addition to the crystal orientation. The domainsinclude a 180° domain and a 90° domain.

In the case where the polarization axis is aligned with the crystalorientation axis, the 180° domain parallel to the applied electric fieldcontributes to polarization, but the 90° domain does not contribute topolarization.

If an ideal ferroelectric capacitor is formed, since the 90° domain doesnot contribute to polarization, a serious problem does not occur even ifthe 90° domain exists. However, the contribution rate of the entire PZTthin film to polarization is reduced by an amount for the existence ofthe 90° domain.

In the actual ferroelectric capacitor, the uppermost surface of theelectrode is not completely flat and has unevenness, and a crystal isgrown in an inclined state in most cases. In this case, the 90° domaindoes not become completely perpendicular to the applied electric field,and is at an angle to the applied electric field to some extent. In thiscase, the 90° domain contributes to polarization. However, since thepolarization axis exists in the direction approximately at right anglesto the applied electric field, a considerably large electric field isnecessary to cause the 90° domain to contribute as the polarization incomparison with the 180° domain. Specifically, it becomes difficult touse the ferroelectric capacitor at a low voltage.

BRIEF SUMMARY OF THE INVENTION

The present invention may provide a ferroelectric thin film which isapplied to a ferroelectric capacitor and has hysteresis characteristicswhich can be used for 1T1C, 2T2C, and simple matrix ferroelectricmemories.

The present invention relates to a ferroelectric thin film formed ofcrystals in which directions of polarization axes are inconsistent withan applied electric field direction in a crystal system.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagram showing configuration of a ferroelectric capacitoraccording to one embodiment of the present invention.

FIG. 2 is a diagram showing the relationship of polarization axes in aPZT crystal according to one embodiment of the present invention.

FIG. 3 is a diagram showing an orientation plane of PZT having atetragonal structure suitable for device application, according to oneembodiment of the present invention.

FIG. 4 is a diagram showing an orientation plane of PZT having arhombohedral structure suitable for device application, according to oneembodiment of the present invention.

FIG. 5 is a diagram showing an orientation plane of PZT having an MPBstructure suitable for device application, according to one embodimentof the present invention.

FIG. 6 is a diagram showing an orientation plane of a bismuth(Bi)-layer-structured SrBi₂Ta₂O₉ suitable for device application, accordingto one embodiment of the present invention.

FIG. 7 is a diagram showing an orientation plane of aBi-layer-structured Bi₄Ti₃O₁₂ suitable for device application, accordingto one embodiment of the present invention.

FIG. 8 shows surface morphology and crystallinity when mixing PbSiO₃into a sol-gel solution for forming PZT, according to one embodiment ofthe present invention.

FIG. 9 illustrates formation of a PZTN thin film by spin coating methodaccording to one embodiment of the present invention.

FIG. 10 shows surface morphology and crystallinity of a tetragonal PZTthin film when mixing PbSiO₃ into a sol-gel solution for forming PZT,according to one embodiment of the present invention.

FIG. 11 is a graph showing hysteresis of a tetragonal PZT thin filmaccording to one embodiment of the present invention.

FIG. 12 is a diagram showing a (100) peak position in a (010) plane withrespect to a (111) peak in the (010) plane of a (111)-oriented PZTsingle crystal, according to one embodiment of the present invention.

FIG. 13 is a diagram showing a (100) peak position in a (010) plane withrespect to a (111) peak in the (010) plane of a (111)-oriented PZTpolycrystalline thin film, according to one embodiment of the presentinvention.

FIG. 14 is a graph showing (100) peak positions when a Phi angle isfixed at 0°, 90°, 180°, and 360° and a Psi angle is assigned from 0° to90° in a (111)-oriented PZT polycrystalline thin film, according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

A ferroelectric memory device according to the present embodiment is aferroelectric memory device which includes a first electrodeelectrically connected with a source or drain electrode of a CMOStransistor formed on an Si wafer in advance, a ferroelectric film formedon the first electrode, and a second electrode formed on theferroelectric film, wherein a select operation of a capacitor formed bythe first electrode, the ferroelectric film, and the second electrode isperformed by the CMOS transistor formed on the Si wafer in advance, anda ferroelectric memory device which includes third electrodes formed inadvance, fourth electrodes arranged in a direction which intersects thethird electrodes, and ferroelectric films disposed at least inintersecting regions of the third electrodes and the fourth electrodes,wherein capacitors formed by the third electrodes, the ferroelectricfilms, and the fourth electrodes are disposed in a matrix, wherein theferroelectric film is a polycrystalline thin film, in which polarizationaxes differ from an axis of an applied electric field, the polarizationaxes are at an arbitrary single angle in a plane perpendicular to theelectric field, and all the polarization axes are nonpolar to theapplied electric field.

A method of manufacturing a ferroelectric memory according to thepresent embodiment includes a step of applying a sol-gel solution forforming a ferroelectric thin film which is a first material solution andcrystallizing the sol-gel solution, wherein the first material solutionis a material solution for forming a ferroelectric layer, is a materialsolution indispensable for forming the resulting thin film as aferroelectric layer, and may include a substance other than a targetferroelectric thin film composition in a crystallization stage. Thisincludes the case where a catalytic oxide which promotes low temperaturecrystallization is formed in a thin film formation stage, and is finallyincluded in the thin film as the thin film constituent element, forexample.

The present embodiment may be applied not only to a ferroelectricmemory, but also to devices utilizing ferroelectricity such as apiezoelectric device and a pyroelectric element.

The ferroelectric memory according to the embodiment of the presentinvention is formed as described below.

FIG. 1 is a view showing a ferroelectric capacitor in a ferroelectricmemory device in the present embodiment. In FIG. 1, 101 denotes a PZTNferroelectric film according to the present invention, 102 denotes afirst electrode, and 103 denotes a second electrode. The first electrode102 and the second electrode 103 are formed of a noble metal elementsuch as Pt, Ir, or Ru, or a composite material containing the noblemetal as a major component. If the element of the ferroelectric isdiff-used into the first electrode, squareness of hysteresis isdecreased due to composition variation at the interface between theelectrode and the ferroelectric film. Therefore, the first electrodemust have a density which does not allow the element of theferroelectric to diffuse into the first electrode. In order to increasethe density of the first electrode, a method of depositing the firstelectrode by sputtering using a heavy gas, or a method of dispersing anoxide of Y, La, or the like into the noble metal electrode is used, forexample. In FIG. 1, the substrate and other constituent elements (MOStransistors and the like) of the ferroelectric memory device areomitted. These constituent elements are described later.

An example of the ferroelectric thin film 101 which is a polycrystallinethin film according to the present embodiment, in which the polarizationaxes differ from the axis of the applied electric field, thepolarization axes are at an arbitrary single angle in a thin film planeperpendicular to the electric field, and all the polarization axes arenonpolar to the applied electric field, is described below.

A first material solution is a solution in which a polycondensationproduct for forming a PbZrO₃ perovskite crystal formed by Pb and Zramong constituent metal elements of a PZTN ferroelectric phase isdissolved in a solvent such as n-butanol in an anhydrous state.

A second material solution is a solution in which a polycondensationproduct for forming a PbTiO₃ perovskite crystal formed by Pb and Tiamong constituent metal elements of a PZTN ferroelectric phase isdissolved in a solvent such as n-butanol in an anhydrous state.

In the case of forming a PbZr_(0.2)Ti_(0.8)O₃ ferroelectric using thefirst and second material solutions, the first and second materialsolutions are mixed at a ratio of (first material solution):(secondmaterial solution)=2:8. The mixed solution was crystallized on a highly(111)-oriented polycrystalline Pt electrode to obtain a PZT thin film,(111)-oriented in the direction of the applied electric field (directionperpendicular to the polycrystalline Pt electrode plane), in which the180° domain among the polarization is arranged in the polycrystalline Ptelectrode plane at an angle of 35.9255° to the polycrystalline Ptelectrode plane, and the 90° domain among the polarization is arrangedin the polycrystalline Pt electrode plane at an angle of 35.9253° to thepolycrystalline Pt electrode plane, and which is spatially nonpolar tothe applied electric field. This enables the 90° domain to beeffectively utilized as the polarization together with the 180° domain.

This is described below using a (111)-oriented PbZr_(0.2)Ti_(0.8)O₃crystal shown in FIG. 2. The polarization axes of tetragonal PZT are(100), (010), (001), (−100), (0-10), and (00-1). FIG. 2 shows thepolarization axes from the (111) direction. For example, if A is apolarization consisting of the 180° domain, A becomes B when thepolarization is reversed. If A is a polarization consisting of the 90°domain, A becomes C or D when the polarization is reversed. Since B andC have almost equal energy, the polarization can be reversed atapproximately the same applied electric field (the actual appliedelectric field differs for the difference 0.0002° between the angles35.9255° and 35.9253° to the Pt electrode plane).

The above example is described using one PbZr_(0.2)Ti_(0.8)O₃ crystalfor convenience of illustration. However, the present invention is noteffective with a single crystal structure. This is because a largedegree of anisotropy exists with respect to the applied electric fieldsince only several polarization axes exist in a single crystal as shownin FIG. 2.

Since the thin film in the embodiment of the present invention is formedof a polycrystal and is arranged in the Pt electrode plane, the thinfilm is stable in energy with respect to the applied electric field anddoes not show anisotropy. Specifically, the polarization s can bereversed at the same time by the same applied electric field.

FIG. 2 shows the (111)-oriented tetragonal PZT single crystal. However,a polycrystalline film is employed in the embodiment of the presentinvention, and crystals are regularly aligned only in the (111)direction. Since the polarization axes are arranged in the plane, thepolarization axes exist infinitely in the actual film. For example, thearranged polarization axes are represented by six vectors in FIG. 3 asdescribed later.

In the case of a conventional PZT thin film used for ferroelectricmemory applications, since the polarization axis is in the (001)direction in the above PbZr_(0.2)Ti_(0.8)O₃ thin film, a highly(001)-oriented thin film in the direction of the applied electric fieldis usually formed. For example, a (001)-oriented Pt electrode is formedon a (001)-oriented MgO single crystal substrate, and a (001)-orientedPbZr_(0.2)Ti_(0.8)O₃ thin film is epitaxially formed on the(001)-oriented Pt electrode. Since PbZr_(0.2)Ti_(0.8)O₃ has polarizationaxes in the (001) direction, the polarization axes are usually alignedin the direction of the applied electric field.

However, the 180° domain and the 90° domain exist inPbZr_(0.2)Ti_(0.8)O₃, and the polarization axis usually means the 180°domain. Since the 90° domain is a domain which exists perpendicularly tothe 180° domain, the 90° domain exists in the (001)-orientedPbZr_(0.2)Ti_(0.8)O₃ thin film perpendicularly to the applied electricfield and does not function as the polarization.

On the other hand, it is impossible to cause the entire polarizationaxes to be oriented in the (001) direction due to occurrence of internalstress in the film or the like. In this case, if the 90° domain existseven at 1%, since the 90° domain becomes a component which is polarizedto only a small extent by the applied electric field as described in thesection on the background art and the problems to be solved by theinvention, a high voltage is necessary to cause the 90° domain whichaccounts for 1% to be reversed. This significantly hinders an increasein the integration and a decrease in drive voltage.

An orientation direction suitable for a ferroelectric polycrystallinethin film generally used for memory applications is described below indetail.

EXAMPLE 1

FIG. 3 shows an orientation plane suitable for device applicationsdetermined for PZT having a tetragonal structure. In FIG. 3, bulk valuesare used as the lattice constant, polarization axis direction (90°domain necessarily exists with the 180° domain), and polarization. Thestate in which the polarization axes infinitely exist in a rotated statein the film plane is shown by using six directions for convenience ofillustration. As candidates for the orientation planes, orientationplanes with high existence probability selected from JCPDS were used. InFIG. 3, the multiplicity means the degree in which the polarization axescompletely overlap when determining the orientation plane suitable fordevice applications using the above parameters. In the case where two ormore polarization axes remain, the higher the multiplicity, the higherthe existence probability. The polarization axis with highermultiplicity effectively contributes to polarization with higherprobability.

As a result, as described in the present embodiment, the effective 90°domain with respect to the actual applied electric field (componentperpendicular to the electric field direction) exists in all theorientation planes other than the (111) orientation plane. Specifically,in the case of using PZT having a tetragonal structure, only the (111)orientation plane is suitable for causing polarization reversal at a lowvoltage or effectively utilizing all the polarization.

FIG. 4 shows an orientation plane suitable for device applicationsdetermined for PZT having a rhombohedral structure. As shown in FIG. 4,the effective 90° domain exists only in (110) in PZT having arhombohedral structure. Therefore, (111), (100), (101), and (001) aresuitable for device applications. However, in the case where low voltagedrive or squareness of hysteresis is required, the angle formed by thepolarization axis and the direction of the electric field is preferablyas small as possible, and the angle formed by the polarization axes ispreferably small in the case where two or more polarization axes exist.Therefore, it is necessary to select (100), (101), or (001)-oriented PZThaving a rhombohedral structure.

PZT with a Zr/Ti ratio of 52/48 is called an MPB region, and tetragonalPZT and rhombohedral PZT are present near this region in a mixed state.FIG. 5 shows an orientation plane suitable for device applicationsdetermined for the case of using the MPB region. In this case, the 90°domain effectively exists in most orientation planes. The 90° domaindoes not exist in only the (111) orientation plane. Since severalpolarization axes exist even if the 90° domain does not exist, it isdifficult to obtain hysteresis with excellent squareness.

FIG. 6 shows an orientation plane suitable for device applicationsdetermined for a bismuth(Bi)-layer-structured ferroelectric SrBi₂Ta₂O₉(SBT). In the case of SBT, it is effective to use a (115), (111), or(110) orientation plane in which the 90° domain does not effectivelyexist.

FIG. 7 shows an orientation plane suitable for device applicationsdetermined for a Bi-layer-structured ferroelectric Bi₄Ti₃O₁₂ (BIT). Inthe case of BIT, it is effective to use a (117), (107), or (317)orientation plane in which the 90° domain does not effectively exist.

A detailed example in which a ferroelectric thin film having theabove-described orientation plane is described below.

EXAMPLE 2

In this example, a PbZr_(0.4)Ti_(0.6)O₃ ferroelectric thin film wasformed.

A conventional method uses a solution containing Pb in an excess amountof about 20%. This aims at preventing volatilization of Pb and reducingthe crystallization temperature. However, since the state of the excessPb in the resulting thin film is unknown, the amount of excess Pb shouldbe limited to the minimum.

A PbZr_(0.4)Ti_(0.6)O₃ thin film with a thickness of 200 nm was formedaccording to a flow shown in FIG. 8 by using 10 wt % sol-gel solutionsfor forming PbZr_(0.4)Ti_(0.6)O₃ (solvent: n-butanol) in which theamount of excess Pb was 0%, 5%, 10%, 15%, and 20%, and further adding 1mol % of a 10 wt % sol-gel solution for forming PbSiO₃ (solvent:n-butanol). FIG. 9 shows XRD patterns and surface morphology of theresulting thin films.

About 20% excess Pb is necessary in a conventional method. However, itwas found that crystallization sufficiently proceeds with the additionof 5% excess Pb. This suggests that excess Pb is almost unnecessary,since the PbSiO₃ catalyst added in an amount of only 1 mol % decreasesthe crystallization temperature of PZT. In the following description, 5%Pb excess solutions were used as solutions for forming PZT, PbTiO₃, andPbZrTiO₃.

A PbZr_(0.4)Ti_(0.6)O₃ ferroelectric thin film with a thickness of 200nm was formed according to a flow shown in FIG. 10 by using a mixedsolution in which 1 mol % of a 10 wt % sol-gel solution for formingPbSiO₃ (solvent: n-butanol) was added to a solution in which a 10 wt %sol-gel solution for forming PbZrO₃ (solvent: n-butanol) and a 10 wt %sol-gel solution for forming PbTiO₃ (solvent: n-butanol) were mixed at aratio of 4:6. As shown in FIG. 11, the resulting hysteresischaracteristics had excellent squareness. This suggests that PbTiO₃ wasfirst crystallized on Pt from the 10 wt % sol-gel solution for formingPbTiO₃ (solvent: n-butanol) by using the solution in which the 10 wt %sol-gel solution for forming PbZrO₃ (solvent: n-butanol) and the 10 wt %sol-gel solution for forming PbTiO₃ (solvent: n-butanol) were mixed at aratio of 4:6. The PbTiO₃ acts as the initial crystal nuclei andeliminates lattice mismatch between Pt and PZT, whereby PZT was easilycrystallized. Moreover, PbTiO₃ and PZT were continuously formed whileforming an excellent interface by using the mixed solution, wherebyhysteresis with excellent squareness was obtained. In addition, sinceall the thin films are single (111)-orientated as shown in FIG. 9,hysteresis having excellent squareness and enabling low voltage drivewas obtained.

A (100) peak position in the plane was investigated with respect to the(111) peak in the (010) plane of the resulting (111)-oriented PZT thinfilm. If the resulting PZT thin film is a single crystal, six pointsindicating (100) should appear as shown in FIG. 12. However, if theresulting PZT thin film is a polycrystal, the position of the (100) peakcannot be specified, and the shape should become circular as shown inFIG. 13. The Phi angle was fixed at 0°, 90°, 180° , and 360°, and thePsi angle was assigned from 0° to 90°. The results are shown in FIG. 14.All had a peak at 54.73°. Specifically, the PZT of the present inventionis a polycrystal, and the polarization axes are arranged at random inthe orientation plane.

1. A ferroelectric thin film formed of crystals in which directions ofpolarization axes are inconsistent with an applied electric fielddirection in a crystal system.
 2. A ferroelectric thin film formed ofcrystals in which directions of 180° domains are inconsistent with anapplied electric field direction in a crystal system.
 3. A ferroelectricthin film formed of crystals in which directions of 900 domains areinconsistent with a direction perpendicular to an applied electric fielddirection in a crystal system.
 4. The ferroelectric thin film as definedin claim 1, wherein the 180° domains are arranged at a constant angle tothe applied electric field direction.
 5. The ferroelectric thin film asdefined in claim 1, wherein the 90° domains are arranged at a constantangle to the applied electric field direction.
 6. The ferroelectric thinfilm as defined in claim 1, wherein the 180° domains reversely rotate ina predetermined electric field with respect to the applied electricfield direction and a ferroelectric thin film plane.
 7. Theferroelectric thin film as defined in claim 1, wherein the 90° domainsreversely rotate in a predetermined electric field with respect to theapplied electric field direction and a ferroelectric thin film plane. 8.The ferroelectric thin film as defined in claim 1, wherein polarizationis arranged at a constant angle to the applied electric field directionhave the same polarization in the same applied electric field.
 9. Theferroelectric thin film as defined in claim 1, formed of a polycrystalhighly oriented in the applied electric field direction in aferroelectric thin film plane.
 10. The ferroelectric thin film asdefined in claim 1, wherein a polarization axis distribution exhibits noanisotropy with respect to the applied electric field direction in aferroelectric thin film plane.
 11. The ferroelectric thin film asdefined in claim 1, using: a tetragonal Pb(Zr,Ti)O₃ ferroelectric whichis (111)-oriented along the applied electric field direction withrespect to a ferroelectric thin film plane.
 12. The ferroelectric thinfilm as defined in claim 1, using: a rhombohedral Pb(Zr,Ti)O₃ferroelectric which is (001)-oriented along the applied electric fielddirection with respect to a ferroelectric thin film plane.
 13. Theferroelectric thin film as defined in claim 1, using: abismuth-layer-structured ferroelectric which is (111) or (110)-orientedalong the applied electric field direction with respect to aferroelectric thin film plane.
 14. The ferroelectric thin film asdefined in claim 1, using: an SrBi₂Ta₂O₉ ferroelectric which is (115),(111), or (110)-oriented along the applied electric field direction withrespect to a ferroelectric thin film plane.
 15. The ferroelectric thinfilm as defined in claim 1, using: a Bi₄T₃O₁₂ ferroelectric which is(117), (111), (107), or (317)-oriented along the applied electric fielddirection with respect to a ferroelectric thin film plane.
 16. Theferroelectric thin film as defined in claim 11, using a (111)-orientedplatinum group metal electrode with a full width half maximum of 2° orless.
 17. The ferroelectric thin film as defined in claim 12, using a(001)-oriented platinum group metal electrode with a full width halfmaximum of 2° or less.
 18. The ferroelectric thin film as defined inclaim 13, using a (111)-oriented platinum group metal electrode with afull width half maximum of 2° or less.
 19. The ferroelectric thin filmas defined in claim 14, using a (111)-oriented platinum group metalelectrode with a full width half maximum of 2° or less.
 20. Theferroelectric thin film as defined in claim 15, using a (111)-orientedplatinum group metal electrode with a full width half maximum of 2° orless.
 21. The ferroelectric thin film as defined in claim 13, using a(110)-oriented platinum group metal electrode with a full width halfmaximum of 2° or less.
 22. The ferroelectric thin film as defined inclaim 14, using a (110)-oriented platinum group metal electrode with afull width half maximum of 2° or less.
 23. The ferroelectric thin filmas defined in claim 15, using a (110)-oriented platinum group metalelectrode with a full width half maximum of 2° or less.
 24. Theferroelectric thin film as defined in claim 16, using an alloy electrodeof lead and platinum group metal.
 25. The ferroelectric thin film asdefined in claim 1, formed by using a mixed solution of a sol-gelsolution and an metal organic decomposition solution.
 26. Theferroelectric thin film as defined in claim 1, comprising silicon, orsilicon and germanium in elements of ferroelectric.
 27. A method ofmanufacturing the ferroelectric thin film as defined in claim 1,comprising: performing crystallization by rapid heating in an oxidizinggas atmosphere at a pressure less than 10 atmospheres.
 28. Aferroelectric memory device using the ferroelectric thin film as definedin claim
 1. 29. A ferroelectric piezoelectric device using theferroelectric thin film as defined in claim 1.